2005 jeep grand cherokee 5.7 hemi acceleration problem - JeepForum.com

 
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post #1 of 8 Old 11-24-2012, 01:16 PM Thread Starter
KyleWRoberts93
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2005 jeep grand cherokee 5.7 hemi acceleration problem

First off id like to start of by saying yes my oil is changed, it is the right weight as well with transfer case fluid both mopar. Now to the issue, When I accelerate at about 35 and up it seems as if its losing power, (I had a magnaflow MUFFLER put on) it sounds as if its a light puttering sound. It continues to accelerate but the RPMs drop tremendouisly and once awhile shudder untill I let off pedal. Now if I step on the pedal a little harder it does climb RPMs but once I let off to just cruise at the desired speed it does the same thing over and over. I do drive it daily and this does happen everytime I drive. I've replaced the PCV valve, the air filter, and cleaned the throttle body. I've read on other forums it could be the egr valve, tps, or crankshaft sensor. Any ideas?? Much appreciated.
2005 jeep grand cherokee limited 5.7 QD2

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post #2 of 8 Old 11-24-2012, 10:11 PM
Walt
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Quote:
Originally Posted by KyleWRoberts93 View Post
First off id like to start of by saying yes my oil is changed, it is the right weight as well with transfer case fluid both mopar. Now to the issue, When I accelerate at about 35 and up it seems as if its losing power, (I had a magnaflow MUFFLER put on) it sounds as if its a light puttering sound. It continues to accelerate but the RPMs drop tremendouisly and once awhile shudder untill I let off pedal. Now if I step on the pedal a little harder it does climb RPMs but once I let off to just cruise at the desired speed it does the same thing over and over. I do drive it daily and this does happen everytime I drive. I've replaced the PCV valve, the air filter, and cleaned the throttle body. I've read on other forums it could be the egr valve, tps, or crankshaft sensor. Any ideas?? Much appreciated.
2005 jeep grand cherokee limited 5.7 QD2
Think the first 2 things I would check are the MAP sensor and EGR valve operation, assuming you do not know the history of the engine. Some readers will display Manifold Absolute Pressure (MAP) and EGR commanded-vs-actual position or EGR error. Eventually, the EGR will generate a code when it fails entirely; however, it can hang up or misbehave within limits beforehand. Mine started acting up at 45K miles. I'm now at 92K on the second one and it has been fine.

MAP should be ~4 psia at idle and 10 psia at highway speeds. (It will reset its base value under WOT acceleration, if you care to try.) EGR valve position may vary between 0% at idle to 50% at 45 mph.

Assuming you use 89 octane gasoline, the knock sensors could be a potential cause. I also watch sparkadvance (~8 degrees at idle, ~20 degrees at cruise, ~38 degrees under acceleration). Not sure how to diagnose them easily without throwing parts at it.

My understanding is that the crankshaft and camshaft position sensors work or they don't.

Can you read the Short Term Fuel Trim (STFT) & Long Term Fuel Trim (LTFT)? They will give clues about the O2 sensors performance.

My '08 has drive-by-wire throttle control, so I do not have any input on the throttle position sensor. Sorry. As for the muffler, I have read reports that a larger exhaust system tends to reduce low-rpm torque but have no specific input here either. Recommend you try to locate a test curve of the new vs stock exhaust system.

Be interested to hear how this turns out. Thanks.

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'08 WK GC Limited. 5.7L HEMI. Quadra-Trac II. Bright Silver Metallic. Class IV hitch.
Michelin LTX M/S tires. Fumoto oil drain valve. Billet Technology oil catch can.
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post #3 of 8 Old 11-24-2012, 11:38 PM
skrach77
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Have you pulled the DTC codes? That can tell you a lot, and give you a place to start from
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post #4 of 8 Old 11-25-2012, 08:30 AM Thread Starter
KyleWRoberts93
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I will look into it. But yes I've had it hooked up to a computer and no codes were able to be pulled.
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post #5 of 8 Old 01-15-2013, 06:02 PM
msailors
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Did you find the solution to the throttle issue? Mine just started acting up this week. If you are cruising down the road at a constant speed, it seems to be an ever so gradual surging. Does it at any speed under a steady cruise speed. Also noticed sometimes when I take off from a red light it's like there is a dead spot and then it kicks in. Does that sound like the problem you had Kyle?
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post #6 of 8 Old 04-15-2013, 12:38 PM
airbag22
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Having similar symptoms in an 07 GCO 90k 5.7L. Any updates?
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post #7 of 8 Old 11-11-2013, 03:49 PM
HoosierDaddie
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Mine does pretty much the same thing as "msailors". Did anyone ever get it figured out. I think whatever mine is doing it is also killing my mileage.
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post #8 of 8 Old 11-11-2013, 09:13 PM
90grandoneer
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Do as Walt recommended, especially the EGR, and then the MAP Sensor, especially if you don't have a catch can. Main EGR symptoms are rough erratic, almost stalling idle, low speed surging/roughness, and poor performance and fuel economy. MAP Sensors are hard to check without onboard monitors, and easier to just replace....less than ~$30. Also, make sure you have a catch can installed.

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